Neofunctionalization of Spilotes sulphureus 3FTx genes has even resulted in the evolution within a single venom of 3FTxs selectively neurotoxic to different prey taxa (mammals or lizards), allowing this non-constricting RFS to take larger mammalian prey. Though this same protein superfamily is commonly found in the venoms of elapid (front-fanged) snakes, no elapid 3FTxs appear to show prey-specific toxicity (with the exception of perhaps Micrurus). Specialized three-finger toxins that target select prey taxa have evolved in some RFS venoms, and this prey capture strategy has appeared in multiple RFS species, from Old World Boiga to New World Spilotes and Oxybelis. New venom protein superfamilies in RFS venoms include matrix metalloproteinases, distinct from but closely related to snake venom metalloproteinases, veficolins, and acid lipases. These venoms have also been discovered to contain several unique venom protein families. In general, RFS venoms share many toxin families with front-fanged snakes, and venoms generally are either a neurotoxic three-finger toxin (3FTx)-dominated venom or an enzymatic metalloproteinase-dominated venom. Rear-fanged snakes (RFS) are a phylogenetically diverse collection of species that feed on a variety of prey and show varying prey capture strategies, from constriction to envenomation. Snake venom research has focused on front-fanged venomous snakes because of the high incidence of human morbidity and mortality from envenomations and larger venom yields of these species, while venoms from rear-fanged snakes have been largely neglected. 2School of Biological Sciences, University of Northern Colorado, Greeley, CO, United States.1Department of Biological Sciences, National University of Singapore, Singapore, Singapore.
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